Research to investigate the interaction of microwave radiation with neural tissue has shown that electromagnetic fields do alter the response of isolated frog sciatic nerves. The threshold for the effect (a reduction in the compound action potential, CAP) occurred at an energy absorption of approximately 4.5 mW/g and the magnitude of the alteration increased with increase energy absorption. Although a decrease in CAP began to occur shortly after initiation of exposure, a significant decrease is not observed until approximately 50 minutes after exposure. Latency, time for the nerve to respond after stimulation, and refractory, the ability of the nerve to respond to a second stimulation, were not affected. These results indicated that the alterations produced by the electromagnetic fields are due to changes in the slow processes such as slow sodium conductance inactivation, potassium conductance inactivation, the activity of Na+-ATPase or other activities that lead to the accumulation or depletion of ions with time constants of the order of 100 milliseconds to seconds rather than fast processes such as fast sodium conductance inactivation with time constants in the order of a few milliseconds. These results plus results from experiments varying temperature of the nerves and blocking K+ channels using TEA (tetraethylammonium), indicate that electromagnetic fields interact with membranes by altering Na+ conductance and/or Na+K+-ATPase activity.